Three is set to confirm it is acquiring O2 in a deal worth £10 billion, with an announcement due to be made on Friday morning.
The deal, first mooted earlier this week, will see Three become the largest mobile network in the UK. It will have a market share of 41%, compared to 32% for EE and 24% for Vodafone.
However, the deal is likely to come under serious scrutiny as it could have major implications for levels of competition in the mobile sector.
In the space of five years, the UK will have gone from having five networks to three.
Three’s owner, Hutchinson Whampoa, has yet to say whether it will keep the O2 brand or decide to merge it with Three in order to make one single provider.
Such a move could cause concern for those who have looked to Three for cheap deals at a time when mobile contracts for top–end flagship devices have started to verge on the unaffordable.
O2 was the subject of interest from BT at the end of 2014, before it decided to pay £12.5 billion to acquire EE instead.